What version of FOG are you running? The simplest method to enforce a replication to begin again is to simply restart the FOGImageReplicator service.
For most this is accomplished by doing: sudo systemctl restart FOGImageReplicator, similarly Snapin Replication would be: sudo systemctl restart FOGSnapinReplicator.
There is currently no way to force a replication to begin via the GUI. This is because the services are at the linux level and run on boot up as root. These FOG Services (FOGImageReplicator, FOGSnapinReplicator, FOGPingHosts, FOGSnapinHash, FOGScheduler, FOGMulticastManager, FOGImageSize) run separately from the GUI environment. That said, you can adjust the times that these cycle via the GUI, and it will receive its information on the next run cycle.